The main charger body type has been used on a number of other bikes (by other manufacturers as well, e.g. Stromer), however your bike uses a Rosenberger connector. Again, a number of other manufacturers (usually high end!) ones, also use the same connector, however it is indeed tricky to find an exact replacement charger or even spare connector.
The two large center pins are obviously the power, however there are also smaller pins that MIGHT carry data (probably CAN bus information).
In something like a Bosch system, a data handshake needs to take place before the battery activates the main power terminals. I'm not 100% certain what the deal is with your A2B bike, which is why I was curious as to whether it worked before, and whether it had been recelled (and whether the recelling operation, also perhaps disconnected the internal data electronics perhaps so the charger was't recognizing it?)
However, I'm > 90% certain that you might still be in luck and the Shima/Alva battery can at least be charged by a third party charger (which doesn't have any handshaking electronics built in). You just need to provide the correct charging voltage to the two big power pins.
I'm afraid I can't point you to a cheap option offhand (although I'm sure they are out there somewhere), however I'm fairly certain Grin Technology's Cycle Satiator works, and they sell (or at least used to!) an adapter to allow a Rosenberger plug to be used.
Let us know how you get on!